This invention relates to electric machines in general and more particularly to an improved two layer cord winding for electric machines such as three phase synchronous generators, which winding produces an improved wave shape with less harmonics.
It is common practice in the winding of three phase electrical machines to use a three zone winding so that the phase voltages will contain no third harmonics. Such three zone windings, which may be of any cord pitch, can also be replaced, to advantage, with six zone, two-thirds pitch windings with unequal zone widths. This results in a reduced coil width and less coil end overhang. In turn, this reduces the amount of copper required and substantially reduces the stray fields at the coil ends. The three zone windings and the six zone windings are both equivalent as far as winding factors and field harmonics are concerned. However, both have the basic disadvantage that even harmonics may appear in the flux which can in turn lead to harmful wave voltages.
One manner of avoiding even harmonics is to use the above described arrangements in a four layer winding. However, this is more complicated to manufacture and requires more space for the slots and coil end insulation. Thus, there is need for a simplified two layer winding such as that described above which will eliminate even harmonics and which may be easily manufactured. In addition, such an arrangement should be possible with any coil width and number of slots and should not have detrimental effects on the other properties of the windings.